Neisseria gonorrhoeae (the gonococcus, gonococci, gc) infects about 2 million civilians a year in the USA, and several millions more in the rest of the world. In women, untreated cervical disease (gonorrhea) often ascends to the endometrium and fallopian tubes to cause pelvic inflammatory disease (PID), which in turn can lead to fallopian tube scarring, sterility and ectopic pregnancy. Each year in the USA, treating gonorrhea, PID and their sequelae costs hundreds of millions of dollars. In addition to helping prevent and treat gonococcal infections and disease and their sequelae, studying gonococcal pathogenesis is important to help us better understand other mucosal pathogens, including those causing serious respiratory and meningeal infections (e.g., meningitis caused by N. meningitidis), and to help us better understand other sexually transmitted diseases. Gonococci grown in vitro interact with host defenses, including serum, epithelial cells and phagocytes, quite differently than do gc grown in vivo. The goal of the research presented in this proposal is to investigate the mechanisms by which gc modulate their lipooligosaccharide (LOS) under conditions thought to exist in vivo, i.e. in the presence of cytidine monophosphate N-acetylneuraminic acid (CMP-NANA) and under decreased oxygen tension (anaerobiosis). We have observed that anaerobiosis acts synergistically with low concentrations of CMP-NANA to induce high level serum resistance in gc. Serum resistance is due (at least in part) to the facile sialylation of LOS by gonococcal sialyltransferase (STase) using host CMP-NANA. We observed that anaerobic gc, compared to aerobic gc, express increased STase activity and altered LOS. To our knowledge, this is the first observation of the regulation of gonococcal virulence factors by conditions thought to exist in vivo (other than iron). To began to explain these observations, I propose the following SPECIFIC AIMS: 1. Develop a rapid, quantitative assay to measure gonococcal sialyltransferase (STase) activity. 2. Identify, clone, sequence and analyze the gonococcal STase gene(s), or genes associated with the expression of STase activity. 3. Purify and biochemically characterize the gonococcal protein(s) responsible for STase activity. 4. Begin investigations to determine the degree, level (transcriptional, translational, or post translational) and mechanism(s) of regulation of gonococcal STase activity or expression by anaerobiosis.